Question

what is the exact value of cos 15

Answer 1

You have to use your calculator, type cos(15)

Answer 2

it can be find out by calculation by using of derivative.

Answer 3

what is the exact value of cos 15

Answer 4

You may have a scientific calculator at home, or here's a nice online one: http://www.ecalc.com/
type cos(15) into the calculator to get the exact value of cos15.

Answer 5

i have to break it down

Answer 6

in steps

Answer 7

Oh. Well I thought you always had to use a calculator. Sorry!
Maybe there's a figure to go along with it?

Answer 8

maybe its ok thank you

Answer 9

we need the exact value, we can use the identity:
\[\cos(A-B) = \cos(A)\cos(B) + \sin(A)\sin(B)\]

let A= 45 and B= 30
from an equilateral triangle we can see \[\cos(30) = \sin(60) = \frac{\sqrt{3}}{2}\]and\[\sin(30)=\cos(60) = \frac{1}{2}\]
and from this right angled triangle we can see that \[\cos(45) = \sin(45)=\frac{1}{\sqrt{2}}\]

put these in the first formula and you can get the exact value